The present invention relates to a ceramic capacitor and ceramic compositions therefor; and, more particularly, to reduction resistive dielectric ceramic compositions suitable for use as a dielectric layer of a ceramic capacitor having internal electrodes made of a base metal such as Ni and a ceramic capacitor fabricated by employing such ceramic compositions as a dielectric layer thereof.
Recently, a base metal, e.g., Ni, is widely used in forming internal electrodes of multilayer ceramic capacitors for the purpose of reducing manufacturing costs. In case the internal electrodes are composed of the base metal, it is required that chip-shaped laminated bodies including therein the internal electrodes be sintered in a reductive atmosphere in order to prevent an oxidization of the internal electrodes. Accordingly, a variety of reduction resistive dielectric ceramic compositions have been developed.
Recent trend towards ever more miniaturized and dense electric circuits intensifies a demand for a further scaled down multilayer ceramic capacitor with higher capacitance. Keeping up with such demand, there has been made an effort to fabricate thinner dielectric layers and to stack a greater number of the thus produced dielectric layers.
However, when the dielectric layers are thinned out, a voltage applied to a unit thickness intrinsically increases. Accordingly, the operating life of the dielectric layers is shortened and thus a reliability of the multilayer ceramic capacitor is also deteriorated.
It is, therefore, an object of the present invention to provide highly reliable dielectric ceramic compositions and ceramic capacitors prepared by employing such dielectric ceramic compositions in forming dielectric layers thereof, wherein the dielectric ceramic compositions exhibit such electrical characteristics as a dielectric constant equal to or greater than 10,000, a capacitance variation of xe2x88x9280% to +30% (based on a capacitance obtained at a temperature of +25xc2x0 C.) in the temperature range from xe2x88x9255xc2x0 C. to +125xc2x0 C., a dielectric loss xe2x80x9ctan xcex4xe2x80x9d of 10.0% or less and an accelerated life of 200,000 seconds or greater.
In accordance with a preferred embodiment of the present invention, there is provided a dielectric ceramic composition comprising: 100 mol part of an oxide of Ba, Ti and Zr, the content of the oxide of the Ba, Ti and Zr being calculated by assuming that the oxide thereof is Ba(Ti1xe2x88x92xZrx)O3; 0.25 to 1.5 mol part of an oxide of Re, Re representing one or more elements selected from the group consisting of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y, the content of the oxide of the Re being calculated by assuming that the oxide thereof is Re2O3; 0.1 to 0.4 mol part of an oxide of Mg, the content of the oxide of the Mg being calculated by assuming that the oxide thereof is MgO; and 0.03 to 0.6 mol part of oxides of one or more elements selected from the group consisting of Mn, V and Cr, the contents of the oxides of the Mn, V and Cr being calculated by assuming that the oxides thereof are Mn2O3, V2O5 and Cr2O3, respectively, wherein a ratio of Ba/(Ti1xe2x88x92xZrx) ranges from about 1.000 to about 1.010 and x in Ti1xe2x88x92xZrx) ranges from about 0.05 to about 0.26.